1. Field of the Invention
The present invention generally relates to optical disk apparatuses, and more particularly to an optical disk apparatus which performs recording and reproduction of data or information on an optical disk having duplicate address identifiers recorded on a sector thereof.
2. Description of the Related Art
Memory media in the form of disks which are replayed by means of laser pickups of optical disk apparatuses are generally used as memory media which store information such as data bases and computer programs. The optical apparatuses include "read only type" apparatuses which can only read out information recorded on disks such as CDs (compact discs) and CD-ROMs, and "read and write type" apparatuses which can also write information on disks. The "read and write type" apparatuses include "write-once type" apparatuses (CD-R) which can write information only once and "erasable type" apparatuses which can write information any number of times such as magneto-optic disk (MO) apparatuses and phase change type disk (PD, CD-RW) apparatuses.
Since the conventional optical disk apparatuses are dedicated to any one of the above types of disks, it is necessary to have a plurality of optical disk apparatuses to replay the various types of disks. In order to avoid such an inconvenience, optical disk apparatuses have been developed which can replay different types of disks. One of such conventional optical disk apparatuses is an apparatus which has a disk cartridge mounted thereon containing CD-ROMs and PD disks.
Such optical disk apparatuses which can be used for both CD-ROMS and PD disks generally consist of an optical head, an optical system control part, a CD system signal processing part, a PD system signal processing part, and a motor driver. The optical head reads out information recorded on a disk or writes information on the disk. The optical system control part performs focus and tracking control of the optical head, drives a laser diode and controls the output power thereof.
Data is recorded with a predetermined format on tracks which are concentrically provided on the optical disk. Each track is circumferentially divided into a plurality of sectors, each of which has a recording area. Each sector is assigned a unique address which is previously recorded on an address area located immediately before the recording area.
FIG. 1 is a diagram illustrating the timing of opening of a read gate in relation to a format of the address area. Each address of each sector has a sector mark area 1 and an ID area 2 at a location immediately before the recording area. The sector mark area 1 contains a sector mark (SM) for identifying a start location of the sector. The ID area 2 has VFO segments in which readout synchronous signals (VFOs) are recorded and ID segments in which an address identifier (ID) indicating the location of the sector is recorded.
When the sector mark (SM) recorded in the sector mark area 1 is read by the optical head, the read gate is opened. Then the readout synchronous signal (VFO) is brought into synchronization with a phase-locked loop (PLL) and an output signal whose phase is synchronized with a frequency modulated carrier is generated. In this phase-locked situation, the sector is in a readable state and thus the address identifier (ID) is read from the ID area 2.
In the case of a conventional optical disk, three VFO segments and three ID segments are alternately provided. In a read mode, if any one of the three address identifiers (ID1 through ID3) has been read, then data can be read from the recording areas. In a write mode, if at least two of the three address identifiers (ID1 through ID3) have been read, then data can be written to the recording area.
Hence, even if the first address identifier (ID1) can not be read, for example, it is possible to identify the location of the sector by reading the second readout synchronous signal (VFO2), the second address identifier (ID2), the third readout synchronous signal (VFO3), and the third address identifier (ID3).
As described above, when the sector mark (SM) has been read, the read gate is opened so that the first readout synchronous signal (VFO1) is brought into synchronization with the phase-locked loop (PLL). However, if the first readout synchronous signal (VFO1) cannot be read due to some defect in the first VFO segment, it is impossible to achieve the synchronization. Therefore, the address identifiers (ID1 through ID3) cannot be read out even if there is no defect in the second and third VFO segments. In this case, a number of attempts will be made to read the address identifier but in vain, and as a result, the corresponding sector is registered as a defective sector because the location thereof cannot be detected. Thus, the sector can no longer be used and the storage capacity of the optical disk is reduced.